Stabilizing aromatic amines



Patented May 10, 1949 2,469,745 STABILIZING ARoMA'rio .AMINES Anthony E. Robertson, Roselle, N. -.I., 'ass igiior' to Standard Oil Development Company, a corporation of Delaware No Drawing. Application June '21, "1946,

"Serial N0. 678,355

This invention relates "to the stabilization of aromatic amines against-deterioration by discol oration, etc., during storage.

Aromatic amines such as aniline, toluidine, xylidine, '.'etc., are normally substantially colorless when freshly prepared or freshly distilled, but tend to darken in .color during storage, the undesirable results being; greatly accelerated by storage-at elevated temperatures.

The object of the present invention is to :st'abilize such aromatic amines against discoloration durin storage.

Broadly, the invention comprises adding to *the aromatic amines .asmall amount of avstabilizer comprising essentially an aromatic biguanide, such as xylyl biguanide, tolyl biguanide, phenyl biguanide, mesityl biguanide, various other aryl biguanides, such as ethyl phenyl biguanide, naphthyl biguanide, anthracyl biguanide, etc. In each of these compounds, the biguanide radical is substituted directly in the nucleus. These compounds may be prepared in various ways. One suitable method is to react a dicyandiamide with the proper aromatic amine. For example, xylyl biguanide is prepared by reacting dicyandiamide with xylidine.

Although the amount of the stabilizer to be used may vary according to the intended duration of storage and the temperature of storage, as well as according to the particular amine and the particular stabilizer used; in general about 0.01% to 1.0% of stabilizer will be sufiicient, and usually about 0.05% to 0.5% by weight of stabilizer will be found most practical for giving satisfactory results.

While the invention is intended to apply broadly to the stabilization of any type of aromatic amines, it is believed particularly applicableto alkaryl amines, especially those having 1 to 3 alkyl carbon atoms. The invention has been found very successful for the stabilization of xylidine, either the pure separate isomers, or mixtures thereof. Other alkaryl amines which may be stabilized include the toluidines, ortho, meta or para, or mixtures thereof, the several ethyl anilines, cumidine (which is isopropylaniline), etc. Dialkylated and trialkylated aryl amines are preferred. Although the invention is particularly applicable to such alkaryl amines,

it may also be used for stabilizing aniline, naph thylarnines, and the various derivatives =of landline in which either -or both or the hydrogen-s of the amino group aresubs'titiited by hydrocarbons, "i. -e., either alkyl or aryl groups, e. g., an N-monomethyl aniline, N-dimethyl aniline, 3N- monoethyl aniline, etc. Thus although the linvention is particularly applicable to alkaryl primary amines, 'other amines such :as secon'dany and tertiary amines may also beiused.

The various "aboVe-rdescribed aromatic amines may be used alone or together with .-a "diluent, such as a hydrocarbon solvent, e. g., naphtha. .Such diluents maybe present in-amounts ranging from only a few percent up to 10, 20 or even 100 times the volume of the aromatic amines, as when such amines are added to gasoline for use as motor fuel.

In carrying out the invention, it is preferred to add the stabilizer to the aromatic amines as soon as the latter has been prepared, or immediately after distillation.

The following experimental data will illustrate the advantages of the invention.

A sample of xylidine (a mixture of various isomeric xylidines) freshly redistilled in an atmosphere of CO2, and which was a light straw color, was tested for color stability by heating in a Staeger oven for 7 hours at 158 C. as an accelerated stability test. At the end of this time the optical density, which is an indication of discoloration or darkening of color, had increased from 0.00 to 0.24. On the other hand, 0.2% of xylyl .biguanide was added to another sample of the same redistilled xylidines and the mixture was simultaneously subjected to the same accelerated stability test. The mixture, which had an optical density of 0.00 at the beginning of the test, was found to still have an optical density of 0.05 at the end of the heating, thereby indicating that the 0.2% of xylyl biguanide had efi'ectively stabilized the xylidine against discoloration during the severe accelerated stability test. Similarly another sample of xylidine to which was added 0.2% of ortho-tolyl biguanide was found to have an optical density of 0.095 after '7 hours. Observations at various periods are shown together with the above results in the following table.

Storage tests on xylidine Optical Density 1 After Storage at 158 F. For Indicated Number of Hours 0.2% Inhibitor None 0.00 0.24 0.77 0.83 1.0 1.02 O-tolyl biguanide 0.00 0.095 0.378 0.46 0.64 0.69 0.84 0.90 1.0 Xylylbiguam'de 0.00 0.05 0.34 0.45 0.68 0.72 0.90 1.0 1.10

1 Helige-Diller photometer-north sky filter.

It is evident from the above data that the discoloration without the stabilizer was several times greater than that which was obtained with the stabilized product.

It is not intended that this invention be limited to the particular materials which have been given merely for the sake of illustration, nor by any theory as to the mechanism of the operation of the invention, but only by the appended claims in which it is intended to claim all novelty inherent in the invention as well as all modifications coming within the scope and spirit of the invention.

The nature and objects of the present invention having been thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A composition of improved stability comprising an aromatic mono-amine containing dissolved therein a small but stabilizing amount of an aromatic biguanide.

2. A composition of improved stability comprising an aromatic mono-amine containing dissolved therein a small but stabilizing amount of xylyl biguanide.

3. The composition of improved stability comprising an aromatic mono-amine containing dissolved therein a small but stabilizing amount of tolyl biguanide.

4. An aromatic mono-amine of improved stability containing 0.01 to 1% of an aromatic biguanide.

5. An aromatic mono-amine of improved sta- 4 bility containing 0.01 to 1% xylyl biguanide.

6. An aromatic mono-amine of improved stability containing 0.01 to 1% of tolyl biguanide.

7. The composition of claim 5 wherein the amount of the xylyl biguanide is between 0.05 and 0.5%.

8. A composition of claim 6 wherein the amount of tolyl biguanide is between 0.05 and 0.5%.

9. Xylidine of improved stability containing between 0.01 and 1% of an aromatic biguanide.

10. Xylidine of improved stability containing between 0.05 and 0.5% xylyl biguanide.

11. Xylidine of improved stability containing between 0.05 and 0.5% of tolyl biguanide.

ANTHONY E. ROBERTSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,221,333 Sibley Nov. 12, 1940 2,263,562 Bigelow Nov. 25, 1941 2,373,021 Downing et al. Apr. 3, 1945 2,410,847 Walters Nov. 12, 1946 2,411,307 Walters Nov. 19, 1946 

